It is known that currently there are communities that aren’t able to access freshwater and that the water suply will soon be at an all-time low, even though our planet is mostly covered in water, 97.5% of this water is salty and only less than 1% is fit for human consumption, these facts make desalination one of the most important processes, but do you really know what it is?
What is desalination?
Seawater has mineral salts that make it brackish and not drinkable for humans, so much so, that if ingested in large quantities can lead to death. Desalination or desalting is the process of removing salt from seawater or brackish water, in order to convert it into drinking water; achieving this is one of the possible Solutions to the shortage of drinking water, since desalination of sea water could provide fresh water for supply and irrigation.
Desalination plants
Desalination plants are industrial facilities for desalination, usually from the sea or salt lakes, to obtain drinking water. Currently seawater desalination plants produce drinking water for many comunities, reaching the amount of over 99 million cubic metres of desalinated water per day worldwide, which provide more than 100 million people with drinking water; but until recently this process was very expensive and therefor reserved for extreme conditions only.
Water Desalination process
Desalination processes are often considered the best way to provide fresh water because they are economical and environmentally responsible.
Technologies used for desalination
There are two types of technologies that are used currently for desalination:
Thermal Desalination
Multistage distillation (MSF)
Multieffect distillation (MED)
Mechanical steam compression (MVC)
Solar distillation
Membrane technologies
Electrodialyses (ED)
Micro, nano and ultra-filtration
Reverse osmosis (RO)
: SWRO (Sea Water Reverse Osmosis) & BWRO (Brakish Water Reverse Osmosis). Most common technology for last years.
Distillation
This process consists of heating water until the point where it evaporates and condensates to obtain fresh water. This type of desalination is performed in various stages where the temperature and pressure decrease until the desired result is achieved.
Freezing
This desalination process freezes sea water in a refrigerated chamber, and it pulverizes it. This results in the formation of ice crystals over the brine, which then is separated to obtain drinking water.
Flash evaporation
In this desalination process, the water is introduced as fine drops into a chamber at below the saturation pressure, converting immediately into vapor and later condensates to form desalinated water.
Hydrate formation
This type of process is not used on a large scale due to its technological difficulties. The process consists of adding hydrocarbons to the saline solution, forming complex crystalline hydrates that are separated to obtain desalinated water.
Electrodialysis
This type of desalination process consists of passing an electric current through and ion solution, making the positive ions migrate towards the negative electrode, while the negative ions head for the positive electrode, meanwhile semi.permeable membranes are placed between both electrodes so that only Na+ or CI- can pass through and the water that is contained in the centre of the electrolytic cell is desalinated and potable.
Reverse Osmosis
Today, Reverse Osmosis (SWRO & BWRO) is the most extensive and advanced desalination system in the world, and it consists of applying pressure to a salt water solution and making it go through a semi permeable membrane that will allow the water to got throught but will stop the dissolved salts in it. The water will flow from the side where the salt concentration is higher to the side where the concentration is lower, resulting in a solution that is minimized in favor of the freshwater.
In Nature, osmosis is a phenomenon that consists in a semi-permeable membrane separating two solutions with the same solvent through which the solvent will pass through leaving the dissolved salts behind, until both sides of the membrane have solutions with the same amount of concentration, this process is carried out without the input of external energy. However, reverses osmosis can be performed thanks to the external application of energy in the form of pressure, overcoming the natural osmotic pressure of the solution.
The pressure required for this water treatment is considerably high. Arflu offers a wide range of Solutions for reverse osmosis plants, especially for the high-pressure stage, where most equipment including but not only valves are made in special materials against corrosion such as Duplex and Super Duplex materials. Being the pressure high as mentioned earlier, note reverse osmosis demands ANSI Class 600 or PN 100 rating valves since working pressure is about 65 to 80 bar.
The most used valve type in the high-pressure stage are the plug valves made in Duplex & Super Duplex. Arflu manufactures RO Plug valves for different service applications into the high-pressure stage of SWRO plants: high-pressure pump discharge isolating and control plug valves, isolating to ERD, CIP service RO plug valves and others.
Arflu has developed some unique (patented) solutions such as the 3 ways plug valve that replaces 2 isolating valves to ERD and CIP & Chick Change solution that allows to replace Teflon sleeve fast, easily and without any technical assistance nor special tooling is required. Arflu also manufactures other valves solutions for Reverse Osmosis such as Ball, Check and Globe Control valves. Would you like to know more about Arflu’s plug valves and its possibilities for desalination plants? Click here.
